bugfix: update_config_from_genesis_json keys
bugfix: update_config_from_genesis_json keys

The keys shouldn't be obligatory.

changwu-tw/pyethapp,gsalgado/pyethapp,ethereum/pyethapp,changwu-tw/pyethapp,gsalgado/pyethapp,ethereum/pyethapp,RomanZacharia/pyethapp,RomanZacharia/pyethapp